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Properties of Graphene Tear-resistant Thermal conductor Very Thin Very stiff, but also flexible Mechanically Strong Stronger than a diamond Electronically conducting 100 times faster than the silicon in computer chips Ductile

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Graphene Becomes a Membrane Graphene is impermeable to all gases due to the electron density of its Aromatic rings In order to create a membrane, must create pores synthetically http://www.physics.upenn.edu/~drndic/group/research.ht ml

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Two Methods for Creating Nanopores Bottom-up synthesis chemical building blocks of functionalized phenyl rings "grow" into a 2-D structure on a silver substrate pore diameters of a single atom pore-to-pore spacing of less than a nanometer

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Graphene Membrane Thinnest possible membrane (1 atom thick) Over 20,000 x thinner than other membranes Ideal pore size for separation Improvement of 500x compared to other membranes Large surface area (Up to areas of 1 mm ^2) Resistant to oxidation (for temperature less than 450 celsius) Very mechanically stable

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Research Article by the Chemical Sciences, Materials Science, and Technology Divisions of Oak ridge National Laboratory (De-en Jiang, Valentino R. Cooper, and Sheng Dai) Article taken from: Nano Letters 2009 Volume 9 No. 12 Pages 4019-4024 All pictures not cited on slide are from this article and belong to the authors

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Article Overview Inspiration for Research No prior research on graphene as a separation membrane Massive possible efficiency gains in the gas separation field Goals Use first principles models to mathematically prove the viability of graphene as the ultimate membrane for gas separation Encourage future research and experimentation Method Density Functional Theory Simulation Results Further Research and Experimentation Ideas

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Research Inspiration Graphene first isolated in 2004 Although there has been a boom of graphene research lately, no efforts have been put into analyzing its usefulness as a gas separation membrane. Gas separation is very energy intensive currently Huge opportunities to increase efficiency Application to other fields Proton Exchange Membranes for fuel cells Carbon sequestration from flue gases Gas sensors in instrumentation

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Research Goals Show Viability of graphene as a gas separation membrane Mathematical modeling from first principles Inspire future research and experimentation New nano-pore designs New nano-pore construction methods Innovative applications to new fields

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Model: Nitrogen Functionalized Graph shows the interaction energy between H 2 and the nitrogen functionalized pore as a function of adsorption height and orientation of the molecule within the pore. Red line and squares are calculated using vdW-DF method. Black line and dots are calculated using PBE method. Relatively flat curve shows little repulsion as molecule approaches the pore.

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Model: Nitrogen Functionalized Graph shows the interaction energy between CH 4 and the nitrogen functionalized pore as a function of adsorption height and orientation of the molecule within the pore. Red line and squares are calculated using vdW-DF method. Black line and dots are calculated using PBE method. Curvature shows the repulsion of the molecule as it approaches the pore

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Model: Nitrogen Functionalized Results Selectivity for H 2 / CH 4 with the nitrogen functionalized pore is 10 8 (Arrhenius) Selectivity is high compared to traditional polymer membranes and silica membranes with selectivities ranging from 10-10 3 Graphene is also much more resilient than other membrane materials that are more susceptible to Hydrogen damage Difficulties Such functionality will be hard to specify during manufacture i.e. The placement of the Nitrogens and Hydrogens will be random around the edge of the pore Much easier to functionalize the poor using only Hydrogen Next calculations are for a Hydrogen only functionalized pore

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Model: Hydrogen Functionalized (a) Face of Hexagonal cell with nano-pore functionalized with only Hydrogen (blue) Created by removing 2 neighboring rings from the graphene sheet like before. (b) Pore-electron density isosurface showing effective pore size Dimensions are now 2.5 Angstroms by 3.5 Angstroms Now it will be harder for both species to pass through

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Model: Hydrogen Functionalized Graph shows the interaction energy between H 2 and the hydrogen functionalized pore as a function of adsorption height and orientation of the molecule within the pore. Red line and squares are calculated using vdW-DF method. Black line and dots are calculated using PBE method. Relatively flat curve shows little repulsion as molecule approaches the pore just like before.

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Model: Hydrogen Functionalized Graph shows the interaction energy between CH 4 and the hydrogen functionalized pore as a function of adsorption height and orientation of the molecule within the pore. Red line and squares are calculated using vdW-DF method. Black line and dots are calculated using PBE method. Curvature shows the repulsion of the molecule as it approaches the pore with values significantly higher than before.

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Model: Hydrogen Functionalized Results Selectivity for Hydrogen over methane raised to 10 23 New barriers were 0.22 eV for H 2 and 1.6 eV for CH 4 which translates to a pass through frequency of 10 9 atoms of H 2 per second at room temperature. Conducted further research to judge the effect of inevitable errors in future manufacture such as removing three neighboring rings versus just 2 resulting in a width of 3.8 Angstroms. Found that this small error resulted in the pore becoming useless (neither species impeded) Demands absolute precision in manufacture

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Conclusions Although these are just mathematical models, they show the viability of graphene as a new generation super membrane material. This research applies universally to the separation of gaseous molecules based on size. If findings can be reproduced in real life, this will seriously advance many industries including green technologies like fuel cells and carbon capture projects. Next efforts should be focused into two main areas: 1. Further modeling to test new pores for more systems of gases 2. Experimentation to physically construct the pores being modeled.

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Further Research As mentioned previously, further modeling and manufacture processes need to be investigated. Interesting Systems to model would be exhaust gases of common combustion engines, air separation, ethylene/ethane, and any other difficult distillation systems Future manufacturing techniques using electron beams to punch holes into graphene need experiments focused on reducing the diameter of the beam to widths capable of targeting groups of 2-3 carbon atoms. New functionalizing groups for liquids Desalination of sea water Wastewater treatment: community and industrial Biological screening This would require functional group modeling that accounts for both mechanical and electrical interactions. Require many different equations for modeling, which will increase the time and computing power needed.

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Literature Cited Article taken from: Nano Letters 2009 Volume 9 No. 12 Pages 4019-4024 All pictures not cited on slide are from this article and belong to the authors.